There is a resin gear with a core metal in which a metallic gear has a synthetic resin part of teeth to engage with another gear, that is, a resin gear with a core metal composed of a metallic sleeve as a core metal and a synthetic resin tooth part covering the outer periphery of the metallic sleeve to reduce the weight of the power transmission gear and suppress noise from the same.
In such a resin gear with a core metal, for reduction of manufacturing costs and improvement of quietness, the tooth part is formed from an outer member with teeth to engage with another gear (gear main body or second molded part) and an inner member that is interposed between the outer periphery of the sleeve and the outer member and is lower in hardness than the outer member (annular member or first molded part) (for example, refer to Patent Documents 1 and 2).
The conventional resin gear with a core metal is manufactured by forming the inner member by injection molding (primary molding) with the metallic sleeve as an insert and then forming the outer member by injection molding (secondary molding) in another cavity molding die, as described in Patent Document 1, FIG. 4, and Patent Document 2, FIGS. 3 and 4.